Mechanisms of Ghrelin Secretion

 描述（由申请人提供）：生长激素释放肽是一种促食欲、调节血糖和抗抑郁的肽类激素，主要来源于分散在整个胃粘膜中的一组不同的生长激素释放肽细胞。其血浆水平在轻度热量限制时升高以刺激食物摄入和脂肪储存，在重度热量限制时升高以防止危及生命的血糖福尔斯下降。Ghrelin水平也会随着心理压力而上升，从而最大限度地减少压力引起的抑郁症并诱导食物奖励行为。生长素释放肽作用的这些关键生理和行为效应通过在生长素释放肽、生长素释放肽受体和/或生长素释放肽O-酰基转移酶缺乏的小鼠模型中观察到的低血糖和抑郁表型来强调，所述小鼠模型在暴露于长期的热量限制或慢性心理社会应激时。尽管生长激素释放肽在葡萄糖稳态和心理社会应激的协调反应中起着关键作用，但对生长激素释放肽分泌的调节机制知之甚少。该建议的中心主题是鉴定在生长素释放肽细胞水平介导生长素释放肽分泌的机制，重点是β 1-肾上腺素能受体（β 1-AR）信号传导。设计这些实验以确定生长素释放肽细胞内的β 1-AR信号传导是否是生长素释放肽对热量限制的反应所必需的，生长素释放肽细胞β 1-AR是否是生长素释放肽对慢性心理社会应激的适当分泌和情绪反应所必需的，以及磷酸戊糖途径和ChREBP（碳水化合物反应元件结合蛋白）介导β 1-AR和葡萄糖对生长素释放肽细胞分泌反应的影响。该提案将利用一种独特的技术和工具来研究和操纵ghrelin细胞。这包括用于离体评估生长素释放肽分泌的分散的胃粘膜细胞的原代培养的系统、当与新的条件性β 1-AR和功能性ChREBP敲除系杂交时允许从生长素释放肽细胞中选择性缺失β 1-AR和功能性ChREBP的生长素释放肽-Cre转基因小鼠、以及报告生长素释放肽细胞的位置并允许荧光激活细胞分选生长素释放肽细胞的生长素释放肽- hrGFP转基因小鼠。这种独特的小鼠品系和技术的收集以及伴随的体内代谢和行为研究、离体分泌实验和其他评估将使我们提出的关于生长激素释放肽分泌和生长激素释放肽对不同极端热量限制、食物摄入和心理社会压力的反应的假设得到严格的检验。最终，希望计划中的研究能促进我们对热量限制和慢性心理社会压力的协调生理和行为反应的理解，以便发现极端体重，慢性压力，抑郁症和饮食失调（如神经性厌食症）的新治疗方式。

 DESCRIPTION (provided by applicant): Ghrelin is an orexigenic, glucoregulatory and antidepressant peptide hormone derived mainly from a distinct group of ghrelin cells dispersed throughout the gastric mucosa. Its plasma levels rise upon mild caloric restriction to stimulate food intake and fat storage and upon severe caloric restriction to prevent life-threatening falls i blood glucose. Ghrelin levels also rise following psychosocial stress, minimizing stress-induced depression and inducing food reward behavior. These key physiologic and behavioral effects of ghrelin action are emphasized by the hypoglycemic and depression phenotypes observed in mouse models of ghrelin, ghrelin receptor, and/or ghrelin O-acyltransferase deficiency upon exposure to prolonged caloric restriction or chronic psychosocial stress. Despite critical roles fo ghrelin in glucose homeostasis and the coordinated response to psychosocial stress, relatively little is known about the mechanisms regulating ghrelin secretion. The central theme of this proposal is to identify mechanisms mediating ghrelin secretion at the level of the ghrelin cell, with a focus on ß1-adrenergic receptor (ß1-AR) signaling. The experiments have been designed to determine if ß1-AR signaling within ghrelin cells is required for the ghrelin response to calorc restriction, if ghrelin cell ß1-ARs are required for appropriate ghrelin secretory and mood responses to chronic psychosocial stress, and if the pentose phosphate pathway and ChREBP (carbohydrate response element-binding protein) mediate the effects of ß1-ARs and glucose on ghrelin cell secretory responses, as hypothesized. The proposal will utilize a one-of-a-kind collection of techniques and tools developed to study and manipulate the ghrelin cell. This includes a system for primary culture of dispersed gastric mucosal cells with which to assess ghrelin secretion ex vivo, ghrelin-Cre transgenic mice which permit selective deletion of ß1-ARs and functional ChREBP from ghrelin cells when crossed with novel conditional ß1-AR and functional ChREBP knockout lines, and ghrelin- hrGFP transgenic mice that report on the location and allow for fluorescent-activated cell sorting of ghrelin cells. This unique collection f mouse lines and techniques and the accompanying in vivo metabolic and behavioral studies, ex vivo secretion experiments, and other assessments will allow our proposed hypotheses regarding ghrelin secretion and the ghrelin response to different extremes of caloric restriction, food intake and psychosocial stress to be rigorously tested. Ultimately, it is hoped that the planned studies advance our understanding of the coordinated physiologic and behavioral responses to caloric restriction and chronic psychosocial stress so that new treatment modalities for extremes of body weight, chronic stress, depression, and eating disorders such as anorexia nervosa may be uncovered.